1. Field
This disclosure relates generally to monitoring changes in a fluid system and, more particularly, to monitoring changes in water content in a hydraulic fluid system.
2. Background
The chemistry of phosphate ester based hydraulic fluid is complex and complicated by the additives that prevent corrosion and provide desirable viscosity and lubricity characteristics. The fluid deteriorates into a fluid that contains phosphoric acid with use and exposure to elevated temperatures above 160° F., which is addressed by acid acceptors added to the fluid. Fluid conductivity (to mitigate streaming charges) is enhanced by the presence of water in the fluid. Nitrogen and oxygen are present in the fluid by exposure of the fluid to the atmosphere. The changes of the fluid due to exposure due to heat, pressure, water and streaming currents can result in chemical changes to the fluid.
Maintaining the correct relationship of fluid additives with exposure of the fluids to water and oxygen prevents adverse reaction of the fluid to these conditions. Monitoring water content to control conductivity to control formation of undesirable reaction products cannot easily be done except by removing a sample from the system for analysis. The chemical changes in the fluid can be affected by exposure of the extracted sample to ambient air, which contains water as a vapor. Extracting a sample of fluid from a hydraulic system to examine it for these elements is difficult because after the sample is being extracted, its chemistry can change due to exposure to ambient conditions. An in-situ method of determining the water and oxygen content of the hydraulic fluid without opening the system to the atmosphere would be desirable.
Various types of complex spectroscopy methods have been previously used to analyze the composition of hydraulic fluid to detect changes in hydraulic fluid chemistry. Detection of out of tolerance chemical conditions using spectrographic methods including Fourier Transform Infrared (FTIR) Spectroscopy are fraught with complexity and are cumbersome for detecting hydraulic fluid water content in an operating hydraulic system.